1. Field of the Invention
This invention relates to an auxiliary lens for changing the focal length of an interchangeable lens of a camera, and particularly to a mount device of the auxiliary lens mounted between the camera and the interchangeable lens.
2. Description of the Prior Art
As an accessory device for changing the focal length of an interchangeable lens, for example, from f=50 mm to f=100 mm, there is already known a rear conversion lens of the type mounted between the interchangeable lens and the camera body. When such a rear conversion lens is used, the minimum F-number of the interchangeable lens as a whole including the conversion lens is increased in accordance with the amount of variation in the focal length.
On the other hand, interchangeable lenses having on the mount thereof means for generating a minimum F-number signal are already known. This F-number signal is applied to and processed by the exposure meter, the shutter speed priority automatic exposure control device or the program automatic exposure control device of a camera. Accordingly, where the aforementioned interchangeable lens and conversion lens are mounted to a camera provided with these devices, malfunctioning or wrong exposure would occur unless the minimum F-number signal of the interchangeable lens is corrected by an amount of variation in F-number and then transmitted to these devices of the camera.